I just went through this.
Your chaincase bearing is probably ok.
To remove your drive shaft you have to remove the chaincase cover. I suggest drilling a 1/4" drain hole (for the oil) in your bellypan right under the bottom of the chain case. Then remove the bolt/washer on the end of the drive shaft.
Then you loosen the axle bolts on your rear wheels and loosen the track tensioner bolts and puch the rear axle forward to put slack in the track. Removing both sets of idlers helps with this as well.
Then you wrestle the skid out. You want help with this. You may want to roll the sled over on it's side, or suspend the rear up off the floor.
Once the skid is out slide/jiggle the driveshaft towards the clutch side until the splined end is free.
If the damage (scoring) to your speedo end is minimal you can probably have a new bearing pressed on but if it's chewed up you'll need to buy a new driveshaft. That's what I had to do. Couldn't find one at my local sled salvage and had to suck up dealer pricing ($268 in Anchorage, AK) but the driveshaft came as a complete assembly with drivers and a bearing.
Since you'll have the track off now would be a good time to either upgrade your track, and/or drivers or to port your track if you were thinking about that.
